The invention relates to a fluid-actuated rotary actuator comprising a housing having a tubular body extending in an axial direction, in which is provided a drive piston assembly for driving a rotatably mounted output shaft which extends perpendicular to the axial direction through the tubular body and the axial end of which is routed out of the tubular body at an upper wall section of the tubular body, further comprising a magnet assembly associated with the axial end of the output shaft and receiving a rotary movement of the output shaft, and further comprising a position feedback device designed to detect the magnetic field generated by the magnet assembly and to provide, in accordance with the detected magnetic field, a position signal corresponding to a position of the output shaft.
A rotary actuator of this type is usually mounted on a valve fitting or a process valve and is used to actuate a valve member of a valve fitting placed in a process fluid for controlling and/or blocking a fluid flow. The output shaft of the rotary actuator is mechanically coupled to a spindle of the valve fitting. The spindle is in turn mechanically coupled to the valve member of the valve fitting, so that the valve member is actuated by way of an actuation of the spindle. The valve member of the valve fitting may, for example, be designed as a flap, throttle valve, cone valve, ball valve or ball cock. By the coupling between the output shaft and the valve member, the position of the valve member is determined by the position of the output shaft.
It is desirable to detect the position of the valve member, so as to be able to better monitor the operation of the valve fitting. Due to the coupling between the valve member and the output shaft, the position of the valve member does not have to be detected directly. Instead, the position of the valve member can be detected indirectly by detecting the position of the output shaft.
Detecting the position of the output shaft of a rotary actuator by means of a position feedback device mounted on the top of the rotary actuator is known from prior art. The position feedback device known from prior art comprises, for example, micro-switches or inductive switches which are actuated via adjustable contact cams in certain positions of the output shaft and which output corresponding signals to a control or management system.
From U.S. Pat. No. 6,135,147, a rotary actuator is known which has a monitoring arrangement mounted on the top of its housing and is used for detecting the position of the output shaft. For this purpose, an indicating device provided with magnets and rotating together with the output shaft is secured to the output shaft, which projects from the housing at the top. In a monitoring arrangement located on the top of the housing adjacent to the indicating device, magnetic switches are provided to apply a current to LEDs as a function of the position of the magnets.